1. Field of the Invention
The present invention relates to a sheet supplying apparatus in which a sheet is separated and supplied from a plurality of stacked sheets and which is used with an image forming apparatus such as a printer, a copying machine and the like.
2. Related Background Art
In conventional image forming apparatuses (for example, printers), there is provided an auto sheet feeder (ASF) as a sheet supplying apparatus for separating and supplying a single sheet from a plurality of stacked sheets (such as paper sheets).
In such an auto sheet feeder, there is provided a sheet supply roller (pick-up roller) or a sheet supply belt for supplying an uppermost sheet or a lowermost sheet from a sheet stack (stacked sheets) while applying a frictional force to the sheet, and, a bank or separation pawl(s) is provided for separating a single sheet to prevent a plurality of sheets from being supplied together with the uppermost or lowermost sheet, or, pads having high coefficient of friction (separation pads) are provided in a confronting relation to the sheet supply roller to prevent the other sheets from shifting together with the uppermost or lowermost sheet.
However, in the above-mentioned conventional techniques, if a surface of the sheet supply roller or the sheet supply belt is degenerated or hardened (due to reduction in coefficient of friction) for long term use, since a frictional force (between the sheet supply roller and the sheet) is reduced not to achieve the proper sheet supply. Further, when paper powder (from the sheet) and/or dirt is adhered to the surface of the sheet supply roller, the frictional force is also reduced not to achieve the proper sheet supply.
In order to eliminate the poor sheet conveyance due to the above causes, the sheet supply roller or the sheet supply belt must be dismounted from the apparatus to clean it or to polish the surface thereof by a grinding sheet kit, the maintenance is worsened.
Further, in recent years, ink jet printers have been developed as compact printers. In such ink jet printers, a sheet having a coating (for example, silica) layer at its recorded surface is sometimes used for the purpose of controlling the ink fixing ability and ink blotting. In this case, the coating material is adhered to the surface of the sheet supply roller in addition to the paper powder to reduce the sheet supplying force to thereby cause the poor sheet supply.